This invention relates to portable space heaters having a deep tank and more particularly to the novel method and apparatus used for transfer of fuel from the tank to the burner nozzle and the return of excess fuel to the tank.
Many types of space heaters have been and are available in the prior art which are designed having two common methods for metering and atomizing the fuel oil in the burner of an oil fired heater. In one type system, fuel oil can be supplied to a nozzle by a fuel pump having a pressure regulator in the line to regulate the nozzle pressures and will operate at approximately 100 psi. In the relatively small type portable heater that is operating in the range of from 30 to 60,000 BTU's, the disadvantage of a fuel pump is the high cost of the pump, for a low priced unit, and the tendency for the nozzle of a unit having a pump to dribble oil into the combustion chamber after the pump and the combustion air fan have been stopped. This dribbling of oil into the hot combustion chamber will cause smoke and an odor from the noxious gas formed from the unburned fuel. It should be noted that steps are taken to prevent such occurrence. This type of fuel pump is shown in U.S. Pat. No. 3,794,461 to Brazee.
The other popular method of supplying oil to the burner of the combustion chamber of a portable heater is through the use of an air aspirating nozzle. Compressed air is metered through the nozzle from a small carbon vane type air compressor. This air compressor delivers the air to the nozzle at approximately 5 psi. As the air passes through the nozzle, a second connection from the nozzle passage is made to the fuel tank below the nozzle. This will cause the oil to be pulled up or drawn into the nozzle where it is then atomized by the air passing through the nozzle and fed into the combustion chamber. This method of metering and atomizing the oil is relatively low in cost and eliminates the problem of oil dripping into the combustion chamber on shut down. However, there are some limitations to the use of this type nozzle system. The fuel flow rate and hence the heat generated by the unit is very sensitive to the depth of the fuel in the tank and the distance between the nozzle per se and the fuel inlet tube opening. Therefore, it has been necessary until now to use only shallow tanks with an air aspirating type nozzle so that the firing rate could be relatively constant as the level of the fuel in the tank is reduced to prevent a substantial change in the oil head. The need for a shallow tank ultimately limits the maximum size of the portable heater's fuel capacity and in general has limited the firing rate to approximately 1.1 gallons per hour. Also, nozzles having an aspirating rate greater than 1.1 gallons per hour are even more limited as to their ability to aspirate liquid with the limited amount of air available from the air compressor on the heater. At 1.6 gallons per hour the ability to lift fuel from the tank is limited to approximately 51/2 inches. It would therefore be physically impossible to supply oil in a shallow tank and have an oil reservoir or tank equivalent to 12 or more hours of continuous operation. The application of this type heater can be on a building construction site or in a farm building. An aspirating type nozzle and a unit having a shallow tank is described in U.S. Pat. No. 4,081,238 issued to Briggs et al.
In view of the above discussion, it is the principle object of this invention to provide a space heater incorporating both an inexpensive positive displacement fuel pump and valve means in conjunction with an aspirating type air nozzle for use on a deep tank type fuel container. Another object of the invention is to raise the fuel from the tank to a particular predetermining heighth in conjunction with the aspirating nozzle. A further object of this invention is to provide an additional path for excess fuel to flow back into the tank. A further object of this invention is to limit the pressure of the fuel in the line from the positive displacement pump so as not to allow excess fuel to be available at the nozzle orifice when the unit is shut down. Another object of this invention is to use the aspirating nozzle principle for bringing fuel from the fuel pump line into the combustion chamber and atomize the fuel for proper combustion.
Another object of the invention is to provide a solenoid operated fuel pump in conjunction with an adjusting valve means to control the pressure and flow of fuel to the nozzle. Another object of this invention is to provide a connection from the fuel line directly to the fuel tank to prevent excess flow of fuel to the nozzle means. Other objects will become apparent to those skilled in the art upon review of this invention and upon reading the description of the preferred embodiment and viewing the accompanying drawing.